1. Field of the Invention
This invention relates to the driving of elements, especially the driving of electron emission elements and the driving of elements whose frequency of response is higher than the ringing frequency of a voltage applied thereto.
2. Description of the Related Art
Two types of elements, namely hot cathode elements and cold cathode elements, are known as electron emission elements. Examples of cold cathode elements are electron emission elements of the field emission type (abbreviated to "FE" below), metal/insulator/metal type (abbreviated to "MIM" below) and surface-conduction type.
Known examples of the FE type are described in W. P. Dyke and W. W. Dolan, "Field emission", Advance in Electron Physics, 8,89 (1956), and in C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976).
A known example of the MIM type is described by C. A. Mead, "Operation of tunnel emission devices", J. Appl. Phys., 32, 646 (1961).
An example of the surface-conduction electron emission element is described by M. I. Elinson, Radio. Eng. Electron Phys., 10, 1290, (1965). There other examples as well, as will be described later.
The surface-conduction electron emission element makes use of a phenomenon in which an electron emission is produced in a small-area thin film, which has been formed on a substrate, by passing a current parallel to the film surface. Various examples of this surface-conduction electron emission element have been reported. One relies upon a thin film of SnO.sub.2 according to Elinson, mentioned above. Other examples use a thin film of Au [G. Dittmer: "Thin Solid Films", 9, 317 (1972)]; a thin film of In.sub.2 O.sub.3 /SnO.sub.2 (M. Hartwell and C. G. Fonstad: "IEEE Trans. E -D. Conf.", 519 (1975); and a thin film of carbon (Hisashi Araki, et al: "Vacuum", Vol. 26, No. 1, p. 22 (1983).
FIG. 16 is a plan view of the element according to M. Hartwell, et al., described above. This element construction is typical of these surface-conduction electron emission elements. As shown in FIG. 16, numeral 3001 denotes a substrate. Numeral 3004 denotes an electrically conductive thin film comprising a metal oxide formed by sputtering and is formed into a flat shape resembling the letter "H" in the manner illustrated. The conductive film 3004 is subjected to an electrification process referred to as "electrification forming", described below, whereby an electron emission portion 3005 is formed. The spacing L in FIG. 17 is set to 0.5-1 mm, and the spacing W is set to 0.1 mm. For the sake of illustrative convenience, the electron emission portion 3005 is shown to have a rectangular shape at the center of the conductive film 3004. However, this is merely a schematic view and the actual position and shape of the electron emission portion are not necessarily represented faithfully here.
In above-mentioned conventional surface-conduction electron emission elements, especially the element according to Hartwell, et al. , generally the electron emission portion 3005 is formed on the conductive thin film 3004 by the so-called "electrification forming" process before electron emission is performed. Electrification forming refers to the formation of an electron emission portion by the passage of current. By way of example, a constant DC voltage or a DC voltage which rises at a very slow rate on the order of 1 V/min is impressed across the conductive thin film 3004 to pass a current through the film, thereby locally destroying, deforming or changing the property of the conductive thin film 3004 and forming the electron emission portion 3005, the electrical resistance of which is very high. A crack is produced in part of the conductive thin film 3004 that has been locally destroyed, deformed or changed in property. Electrons are emitted from the vicinity of the crack if a suitable voltage is applied to the conductive thin film 3004 after electrification forming.
The surface-conduction electron emission element mentioned above is particularly simple in structure and easy to manufacture and therefore is advantageous in that a large number of elements can be formed over a large area. Accordingly, research has been directed to a method of arraying and driving a large number of elements, as disclosed in Japanese Patent Application Laid-Open No. 64-31332, filed by the applicant.
Further, applications of surface-conduction electron emission elements that have been researched are image forming devices such as image display devices and image recording devices, as well as charged beam sources, etc.
As for applications to image display devices, research has been conducted with regard to such devices using, in combination, surface-conduction type electron emission elements and phosphors which emit light in response to irradiation with an electron beam, as disclosed, for example, in the specifications of U.S. Pat. No. 5,066,833 and Japanese Patent Application Laid-Open (KOKAI) No. 2-257551 filed by the present applicant. The image display device using the combination of the surface-conduction type electron emission elements and phosphors is expected to have characteristics superior to those of the conventional image display device of other types. For example, in comparison with a liquid-crystal display device that has become so popular in recent years, the above-mentioned image display device emits its own light and therefore does not require back-lighting. It also has a wider viewing angle.